Patient Safety Concerns in Diagnostic Radiology? Lawrence T. Dauer, PhD, CHP Assistant Attending Health Physicist Department of Medical Physics RAMPS/GNYCHPS Spring Symposium April 30, 2010
Benefits? 3
Background Radiation in U.S. ~6.3 msv/yr ~0.02 msv/day (~2 mrem/day) NCRP 4
Absorbed Dose Equivalent Dose 5
Risk Evaluations ations Monte-Carlo transport and energy deposition Equivalent Dose Age-AdjustedAdjusted Gender-Adjusted Organ risk factors 6
Effective Dose ICRP-103 (2007) 7
Internal Radionuclide Radiation Dosimetry MIRD Formalism Absorbed fractions and S factors from reference anatomic phantoms (Medical Internal Radionuclide Dosimetry) S (r k r h ) 8
Doses in CT ESD CTDI DLP = CTDI x L E/DLP for adults: ACR, 2004 Head 0.0023 Neck 0.0054 Chest 0.017 Abd 0.015 Verdun, 2008 Pelv 0.019 9
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Radiation Passport 1.0 iphone application 11
Typical Radiation Doses - General Radiology Examination Effective Dose msv Dental 0.05 (0.02-0.09) 0.09) Chest 0.1 01(0 (0.02-0.81) 02 0.81) 081) Head 0.1 01(0 (0.1 1-0.22) Mammography 0.7 (1-3 gland) Abdomen/Pelvis 1.2 (0.7-1.2) See http://mskweb5.mskcc.org/intranet/html/65927.cfm For a complete listing of typical radiology doses 12
Typical Radiation Doses - Computed Tomography Examination Effective Dose msv PET Attenuation (CT Only) 0.72 Head 2 (0.8-5) Chest 7 (4.6-20.5) Abdomen or 10 (6-27.4) Pelvis CT Angiography 13 (4.6-15.8) 13
Typical Radiation Doses - Nuclear Medicine Examination Effective Dose msv F-18 FDG 15mCi (Nuclear Med only) I-131 MIBG 1mCi 7.5 Tc-99m pertech. 5 Tc-99m stress 6 I-131 therapy 270 9 RADAR 14
Typical Radiation Doses Fluoroscopy Entrance Skin Dose Examination Skin Dose mgy Hepatic Embolization Arterial Embolization 2000 (1251-9500) 3000 (1761-8073) ED~60 msv Biliary Drainage 660 (401-3569) Dauer, Thornton JVIR 2009 IVC Filter 260 (162-2686) 2686) Mediport Chest 12 12 (8-620) 15
70 60 50 40 Head CT 200 m A s B ra in B o n e B o n e m a rro w Thyroid 30 Dose (mg Gy) Organ 20 10 0 25 20 15 Abdom inal C T 200 m A s S tom ach Liver O v a rie s C o lo n B o n e m a rro w 10 5 0 0 10 20 30 40 50 60 70 80 Age at C T Exam ination (Years) *Adapted from Brenner et al. 2001 16
Lee, 2007,MedPhys 17
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Tube Current [ma] 500 400 300 200 100 0 Lumbar Spine Auto Exposure control o Slice Number Tube Cu rrent [ma A] 600 400 200 0 Chest Slice Classification: Unclassified 19
How do we assure quality control on an ongoing basis? Medical Physicist verifies CT dose on new equipment prior to 1 st patient use, at least 1x per year and at x-ray tube changes. CT dose measurements meet American College of Radiology, State, and Local guidelines for dose. CT machine settings are developed by Radiologists and Radiology specialists. Technique Charts showing machine settings and standard delivered doses are posted at each CT.
Quality Control - Standard ACR Phantoms Erdi, 2010 - MSKCC data 21
Variability in CT doses for real individuals Mean 13-fold variation Between highest to lowest dose For each study type 22
Machine Model & Type = 2.5 to 5-fold variation DLP E MSKCC - Prins, et al, 2010 23
Ongoing g Evaluations
Principles of Radiation Safety Justification in Radiology Benefit greater than risk Optimization Benefit AHARA Risk ALARA Limitation Occupational doses based on risk of safe industries 25
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Can We Predict Effects at Low Doses? While moderate/high doses cause well-documented effects, we cannot measure significant effects at the doses where typical diagnostic or regulated doses occur. Effect? 25 250 500 Dose (msv) 27
Classic Risk Paradigm Energy deposited in the nucleus Ionizations produced DNA broken CANCER Mutations Chromosomal Aberrations Cell Death Cell Transformation
Expanded Risk Paradigm Energy deposited in the nucleus OR cytoplasm GENETIC SENSITIVITY Ionizations produced Epigenetic factors DNA Damage Other Proteins PCNA, RPA TISSUE and APE RESPONSE Oxidative Status Up regulation of antioxidant enzymes Inhibition of superoxide anions Adaptive Response CANCER??? Bystander biological Modifies Effects GENE AND PROTEIN EXPRESSION DNA may be broken, or other molecules les may be damaged Genomic Instability Triggers biological processes SIGNALING Direct Cell-cell Indirect secreted or shed Signaling molecules ++ Ca DNA-PKc s TGF-B
Need an Expanded Paradigm for Low-Dose Response Production of damage Linear processes Deposition of energy DNA damage Physics Responses to damage Non-linear processes Induction of Apoptosis Gene & Protein expression Biology
Evaluation Conclusions Vary BEIR VII - NAS Available biological and biophysical data supports a linearno-threshold (LNT) risk model. ICRP 99/103 While existence of a low dose threshold may be likely for radiation related cancers in some tissues, the evidence does not support a universal threshold. DDREF-modified LNT suggested as prudent. French Academy New radiobiology focus. Biological differences at high vs. low doses. LNT overestimates risk at low doses.
Low Dose - Linear Risk Model Exposed Population (~5% per Sv) ICRP-103 for cancer and heredity effects Cancer Heredity Effects Total Whole 5.5 0.2 5.7 Adult 4.1 0.1 4.2 A statistically significant increase in cancer has not been detected in populations exposed as adults to doses of less than 50 msv. No hereditary effects in atomic bomb survivor offspring. 32
~ Patient Risks Risk of contracting cancer increased by less than ½% 50 msv Temporary Sterilization (Men) 150 mgy Temporary blood count change 250 msv Cataract <1000 mgy Permanent Sterilization ti (Women) 2500 mgy Skin Erythema (reddening) 3000 mgy 33
Fetal Radiation Risk Most Risk 1 st Trimester No Malformations <100mGy No Malformations 100-1000mGy 1000mGy 3 rd Trimester Termination of pregnancy n at <50 mgy is NOT justified based upon radiation risk Take care - especially during multiple pelvic CTs, long fluoro, or radiotherapy Wagner, ICRP, IAEA, ACOG Most risk Less Least 34
ICRP-103 on Individual id Risks it remains the policy of the Commission that its recommended nominal risk coefficients should be applied to whole populations and not to individuals [and] believes that this policy provides for a general system of protection that is simple and sufficiently robust (p.55) 35
If dose is < 100 msv Take Care When Attempting to Assign Quantitative Risk to Individuals 36
Have we evaluated total imaging doses for our patients? All patients N=68 1997 cohort N=43 2002 cohort N=25 1997 vs. 2002 p-value 5y Cumulative ED, msv 4.56 (3.3-54.4) 4.65 (3.5-62.3) 4.55 (3.3-50.2) 0.56 Annual 092 0.92 097 0.97 091 0.91 085 0.85 ED, msv (0.7-11.0) (0.7-12.5) (0.7-10.9) Annals of Surgical Oncology - pending 37
Are Diagnostic Doses Really a Concern for Our Patients? Risks models based on dose averages and large populations. p Risk vs. Benefit to Individual. Benefit must always be considered. Justification and Optimization are paramount 38
Justification In most symptomatic adults, radiation doses for diagnostic radiology procedures, including CT scans, result in extremely small risk, ik typically well-justified by the medical need. Risks are ~ 2-3 x larger for children. 39
Suggestions NO radiation when you don t do the exam! Ensure each exam is justified. Carefully scrutinize screening protocols for healthy subjects and post-therapy therapy screening protocols for pediatric patients and patients with long-term survival expectation. Communicate dose and risk with staff (especially referring physicians) and patients. Medical Physics review/testing of final machine std protocols!! 40
Research Challenges Some Questions Still Need Answers Human Chromosomes Showing DNA Damage From Radiation - Photo Credit: Massey University Molecular markers of DNA damage at low doses? DNA repair fidelity and capacity for double and multiple strand breaks at low doses? Adaptation, hypersensitivity, bystander effects, hormesis, and genomic instability for radiation carcinogenesis? How to best communicate risk with patients? Benefits? 41
RHI Radiation Hazard Index (RHI) ED Range Background Equivalent Typical Examples Risk Category 10 10,000Sv - Industrial Uses 10 +2 Greater 9 1000Sv - Food Irradiation 10 +1 Great 8 100Sv Centuries Radiotherapy: dose to tumor 7 10Sv Century Acute Total Body GI / Bone Marrow 10 0 Major 10-1 Major 6 1Sv Decades Increased Ca Risk 10-2 Strong 5 100mSv Decade Dose Limits 10-3 Moderate 4 10mSv Years CT Nuclear Med Diag 10-4 Low 3 1mSv Months Abdominal x-ray 10-5 Very Low Dauer,2008 2 01mSv 0.1mSv Weeks Chest x-ray, 10-6 Minimal Mammography 1 0.01mSv Days Bone Density, Skull ~0 Negligible 42
Research Challenges What Data are still Needed? DNA Ligase Repairing Damage Prospective cohort and nested case-control control studies of moderate- dose medical exposures. Epidemiological study consortia for medically exposed populations (CTs, Pediatrics, IR). Occupational low-dose studies. Exposed Population studies. Current Policies justified and optimized themselves? 43
Lawrence T. Dauer, PhD, CHP Assistant Attending Health Physicist Department of Medical Physics, MSKCC dauerl@mskcc.org American Association of Physicists in Medicine